varying vec4 diffuse,ambient;
varying vec3 normal,lightDir,halfVector;

void directionalLighting()
{	
  /* first transform the normal into eye space and 
  normalize the result */
  normal = normalize(gl_NormalMatrix * gl_Normal);
  
  /* now normalize the light's direction. Note that 
  according to the OpenGL specification, the light 
  is stored in eye space. Also since we're talking about 
  a directional light, the position field is actually direction */
  lightDir = normalize(vec3(gl_LightSource[0].position));

  /* Normalize the halfVector to pass it to the fragment shader */
  halfVector = normalize(gl_LightSource[0].halfVector.xyz);
        
  /* Compute the diffuse, ambient and globalAmbient terms */
  diffuse = gl_FrontMaterial.diffuse * gl_LightSource[0].diffuse;
  ambient = gl_FrontMaterial.ambient * gl_LightSource[0].ambient;
  ambient += gl_LightModel.ambient * gl_FrontMaterial.ambient;
}